Frequency stable multivibrators



sept'. 11, 1956 s. SHARIN ETAL 2,762,917

FREQUENCY STABLE MULTIVIBRATORS Filed Aug. 7, 1955 @HAN/7i J.' A75/W BY@da United States Patent FREQUENCY STABLE MULTIVIBRATORS Samuel Sharinand Arthur E. Canfora, Brooklyn, N. Y., Anthony Liguori, Hackensack, N.J., and Hajime J. Kishi, New York, N. Y., assignors to Radio Corporationof America, a Delaware corporation Application August 7, 1953, SerialNo. 372,891

12 Claims. (Cl. Z50- 36) The invention relates to multivibrators, andparticularly pertains to means for stabilizing the output frequency ofsuch multivibrators.

It is known that the output frequency of multivibrators depends on suchfactors as the variation of D. C. anodeto-cathode resistance, and thevariation in grid cut-off voltage of individual electron dischargedevices of a given type, the change in D. C. anode-to-cathode resistanceand the change in grid cut-off voltage of a given electron dischargedevice due to aging, as well as the time constant of the circuit.

It has been proposed to regulate the operating supply potentials and theclamping of portions of the multivibrator circuit to predetermined fixedpotential levels during part of the operating cycle in order tostabilize the output frequency.

An object of the invention is to reduce the effect of the D. C.anode-to-cathede resistance, and the grid cutolf voltage values on theoutput frequency of a multivibrator and thereby render the outputfrequcncy`de pendent solely upon the time constant of the circuit.

Another object of the invention is to prevent the replacement ofdischarge devices of a given type from adversely affecting the frequencyof operation of a multivibrator.

A further object of the invention is to minimize or prevent the effectsof normal aging of the electron discharge devices used in amultivibrator from affecting the frequency of operation.

Still another object of the invention is to provide a multivibratoraffording more stable frequency division by larger numbers than ispresently possible with conventional multivibrators.

The objects of the invention are attained by means of a pair ofcross-coupled electron discharge devices, arranged so that conduction isalternated between the two discharge devices under the control of otherelectron discharge structures, preferably having a grid voltageV cutoffcharacteristic substantially lower than the grid voltage cut-offcharacteristic of the cross-coupled electron discharge devices,individually coupled between the anode and control electrodes of each ofthe cross-coupled electron discharge devices.

In order that the invention may be more clearly understood and readilyput to practical use, one circuit arrangement embodying the invention ishereinafter described, by way of example only, with reference to theaccompanying drawing, in which:

Fig. l is a schematic diagram of a general embodiment of the invention;

Fig. 2 is a graphical representation of the mode of operation of aportion of the circuit shown in Fig. l, useful in explaining theoperation thereof.

Referring to Fig. l, there is shown a multivibrator according to theinvention having an output frequency which is extremely stable. A pairof electron dischargel devices 11, 12 having cathodes 13, 14, grids 15,16 and anodes 17, 18 respectively have unidirectional operating potenicetials applied thereto from a source (not shown) which is preferablyregulated but not necessarily so. The anodes 17, 18 of the devices 11and 12 are connected to the positive terminal of the operating potentialsource by means of anode resistors 21 and 22, while the grids 15, 16 areconnected to the negative terminal of the operating potential source bymeans of grid resistors 25, 26. The cathodes 13, 14 are connected to asource of potential -k which is negative with respect to a point offixed reference potential or ground which, in turn, is electricallyintermediate the positive and negative terminals of the operatingpotential source. The voltage on the cathode 13, 14 is preferably setfor the type of electron discharge device used so that, even in theworst possible case of anode-to-cathode resistance variation due toaging of the discharge device, the potential at the anodes 17, 18 willtend to go below groundv when the devices 11, 12 conduct.

The electron discharge vdevices 11 and 12 are crosscoupled inconventional manner to form a reciproconductive circuit 30. As employedherein, the term reciproconductive circuit is construed to include alltwo electrode structure regenerative circuit arrangements in whichconduction alternates in one or the other electrode structure. Whenconsidering the free running or astable circuit, the term is synonomouswith the broad term multivibrato-r, which term is herein limited to theastable reciproconductive circuit. rlfhe monostable reciproconductivecircuit (sometimes referred to as a self-restoring trigger circuit),which requires one triggering pulse to switch from the single stablestate of conduction to the singleV unstable state andV return, isoccasionally referred to as a monostable multivibrator and more oftenreferred to as a trigger circuit, which latter term is sometimes usedfor a stable reciproconductive circuit. The bistable reciproconductivecircuit, which is one which requires two triggering pulses to switchfrom one stable state to the other stable state and return, is sometimestermed al locking circuit; bistable multivibrator; or, according to use,a binary circuit.

As shown in Fig. 1, the electron discharge devices 11 and 12 are crossconnected by means of networks cornprising resistors 31, 32 andcapacitors 33, 34 to formi a bi-stable reciproconductive circuit,capable of operating in the conventional bistable mod` In many instancesthe capacitors 33, 34 maybe omitted without affecting the mode ofoperation to any practical extent. Diodes' 35 and 36` are connectedbetween the anodes 17,-18 of' the electronv discharge devices 11 and 12respectively and ground in order to clamp the anodes to ground when therespective electron discharge device is conducting, thus holding theanode voltage swing constant and in'- dependent of the D. C. anoderesistance. Triggering of the reciproconductive circuit 30 isaccomplished according to the invention by a pair of triggering electrondischarge structures 41 and 42,. each including respective cathodes 4Sand 46 at ground potential and control electrodes 51 and 52, coupled tothe anodes of the devices 11 and 12 by capacitors C1v and C2,respectively. The grid electrodes 51 and 52 are connected to thepositive terrninal of the operating potential sourceby means ofresistors R1 and R2, respectively. Anode potential is obtained by meansof voltage dividers comprising resistors S3, 55 andV 56, 57 connectedbetween ground' and theI positive terminal of the operating potentialsource.` The anodes 61, 62 of the triggering structures are vcoupled tothe grids 15, 16 of the controlled electronV discharge devices 11, 12 bymeans of couplingv capacitors 65 and 66, respectively. According to theinvention, the cut-olf voltage' the corresponding electron dischargedevice 11, 12, and

3 the potentials at the anodes 61, 62 are made low with respect to thepotentials at the anodes 17, 18. The voltage dividers comprising theresistors 53, 55 and 56, 57 coupled to the anodes 61 and 62 of thestructures 41 and 42 are used to lower the absolute cut-off voltagesrequired for the triggering structures 41 and 42 by lowering theeiective anode operating supply. The components associated with thereciproconductive circuit in and of itself are chosen so as to obtaintriggering and clamping action according to the practiced art.

In explanation of the operation of the circuit of Fig. l, it is assumedthat a transition is just occurring such that the reciproconductivecircuit device 11 is just starting to conduct, and the device 12 is juststarting to block. The voltage at the anode 18 of the controlled device12 will rise to a value determined by the relative values of the voltagedivider comprising the resistors 22, 32 and 25 and the value of theoperating potential supplied according to the formula where E is theoperating potential applied between minus and (-1-) plus. This isfollowed by the complete blocking of the device. The positive swing ofthe anode 18 of the device 12 is coupled to the grid 52 of the triggerstructure 42 which already is conducting. Since the structure 42 isconducting, the coupled positive swing causes no change in the state ofconduction of the device 42. At the same time that the voltage at theanode 18 of the device 12 is rising, the voltage at the anode 17 of thedevice 11 is faling toward a negative value due to the device 11conducting. The voltage at the anode 17 of the device 11 cannot go to anegative value, due to the clamping action of the diode 35, but isstopped at ground. This limited negative swing of the anode 17 of thedevice 11 is coupled to the grid 51 of the trigger structure 41, whichhas been conducting. The trigger structure 41 is thusdriven to cut-oipermitting the anode voltage to rise. Now this stable state ofconduction of the device 11 and the structure 42 and the non-conductingstate of the device 12 and the structure 41 exists for a time, t1,determined by the values of the resistor R1 and the capacitor C1 afterwhich the capacitor C, associated with the triggering structure 41, isdischarged and the grid 51 of the structure 41 rises to the cut-offvoltage. The structure 41 then conducts and the anode 61 goes in anegative direction. This negative swing is coupled to thereciproconductive circuit 30 at the grid 15 of the device 11. Thereciproconductive circuit 301 changes state so that the device 11 isnon-conducting and the device 12 is conducting. The negative swing atthe anode of the device 12 drives the triggering structure 42 intocut-oit for a time t2, determined by the values of the resistor R2 andthe capacitor C2, after which the capacitor C2 associated with thestructure 42 is discharged and the grid 52 of the triggering structure42 rises to the cut-oi voltage. The triggering structure 42 conducts andthe anode 62 goes in a negative direction. This negative swing iscoupled to the reciproconductive circuit 30 at the grid 16 of the device12 and the entire cycle is repeated as described above.

A graphical representation of the waveform obtained at the grid 51 isshown in Fig. 2. The zero voltage axis is represented by the broken line81; the cutoff voltage level by the dashed line 83; and the positiveoperating potential level by the dashed line 85. The'heavy line 90represents the voltage variation of the grid 51 with respect to time.The other grid will exhibit the same voltage variation but displaced intime by the period t1, and the waveform at this grid is thereforeomitted. The charging curve 91 of the capacitor C1 follows the usual lawand if allowed to charge fully would follow the broken curve 93. Thetime constant of the capacitor C1 and the resistor R1 determine the timeperiod t1. Like- 4 wise the values of the capacitor C2 and the resistorRz determine the period tz. These time periods may be made equal byusing equal values of resistors and capacitors, or, if an asymmetricalor unequal duty cycle Wave is desired, different values may be used.

The output square wave maybe taken from either anode 61 or 62, butpreferably it should be taken from the anodes 17, 18 as the waveformwill be somewhat better. The circuit arrangement as shown in Fig. 1 willnot start to oscillate on noise potential, but must be pulsed. Thestarting pulse may be applied at one of many points; for example, theanodes 61, 62; the grids 51, 52;,the anodes 17, 18; or the eathodes 13,14 provided a diode element having a nite back resistance characteristicis interposed in the cathode lead of the tube that is pulsed.

The circuit arrangement according to the invention may vary from thatshown in Fig. l. The simplest variation is obtained by omitting thespeed up capacitors 33, 34. The reciproconductive circuit 30 will stillbe bistable.

The results obtained for low frequency operations willy remain the same,but at the higher frequencies, phase shift problems will be encounteredso that the triggering will become less stable.

The reciproconductive circuit 30 can be connected for monostableoperation -by omitting the cross-coupling resistor 33 orthecross-coupling resistor 31. The speed up capacitor 32 or 34 may beretained for short time period operation, otherwise it may beeliminated'alsoj. The non-conductive tube is then pulsed to start themultivibrator circuit arrangement to oscillating. This circuitarrangement will always be started in the same phase relationship, afeature which is important for many telegraph and counting applications.

A free running multivibrator arrangement, not requiring any startingpulse, is obtained on converting the reciproconductive circuit 30 to theastable form by omitting the cross-coupling resistors 31, 32. Thisvariation, as in each of the other circuit modiiications, operates inthe same manner as the complete circuit arrangement shown in Fig. 1insofar as the triggering function is concerned. v

Because the monostable reciproconductive circuit requires only onecritical timing circuit, the improved results according to the inventionmay be obtained a monostable circuit, with one-half of the circuitarrangement shown in Fig. 1. For example, the portion of the circuitcomprising the tubes 11, 35 and 41 and associated components with thecross-coupling networks 31 33 aud 32-34 disconnected and a resistiveelement connected between the anode 61 and the grid 15 can be itriggered to the unstable state by application of a triggering pulse tothe anode 17, the grid 51, or the anode 61. This circuit will thenreturn to the stable state after a time depending on the values of theresistor R1 and the capacitor C1. The RC circuit in this instancefollows the same law as in the conventional reciproconductive circuits..

The voltage swings and cut-off characteristics are `Clifferent, ofcourse, to provide the improved results.

The circuit arrangement according to Fig. 1 can be used as a frequencydivider which exhibits improved'performance. Positive pulses applied tothe grids 51 or 52 at given recurrence rate will produce square waves ofsub-multiples of that rate at the -anodes 17, 18 of the controlled tubes11, 12. If an output pulse train is re-4 quired, conventionaldilerentiatingand shaping circuitry can be used in known manner.V

The frequency of operation of Fig. 1 is about 600 C. P. S. for R1=R2=1megohm and C1=C2=ll65 micro-micro-farads. It should be noted that thevalues for R1 and C1, associated with one-half of the circuit, need notbe equal to the values for R2 and C2 for the other half, unless asymmetrical wave shape is desired. Any pulse rate with any pulseinterval is possible'within the range of such multivibrators aspracticed in the art.A The-following values of other components wereused inv a circuit in accordance with the arrangement of Fig. 1 asoperated and tested at 600 C. P. S.

Resistors Ref. No.: Value 21, 22 kilohms-- 75 25, 26 megohms 2.0 31, 32do 2.7 53, 55, 56, 57 kilohms 100 Capacitors Ref. No.: Value 65, 660.001 pid. Speedup capacitors 33, 34 were not used.

Tubes Ref. No.: Type 11, 12 5963 35, 36 6AL5 41, 42 12AX7 Positiveoperating potential of 150 volts regulated was applied between groundand those points of the circuit marked by the plus sign and negativeoperating potential of 150 volts was applied between ground and thosepoints marked by the minus sign, with the cathodes 13 and 14 fixed at avalue of 371/2 volts with respect to ground.

The invention claimed is:

l. A monostable multivibrator circuit including an electron dischargedevice having at least cathode, grid and anode electrodes, and having agiven cut-off gridvoltage characteristic, an anode resistor and a gridresistor coupled in series with the individual grid-anode path of saidelectron discharge device, means to apply positive operating potentialbetween said anode resistor and a point of iixed reference potential,means to apply negative operating potential between said grid resistorand said point of iixed potential, means to apply a potentialintermediate the fixed and negative potentials to the cathode of saidelectron discharge device, an electron discharge structure having acathode, a grid and an anode and having a cut-oft' characteristic gridvoltage substantially less than that of said electron discharge device,means to connect the cathode to said point of fixed reference potential,an anode resistor connecting the anode of said electron dischargestructure to said means to apply positive operating potential and tosaid point of fixed reference potential, means coupling the anode ofsaid electron discharge structure to the grid electrode of said electrondischarge device, and a return time determining network coupling theanode electrode of said electron discharge device to the grid of saidelectron discharge structure, said network comprising a capacitorconnected between the coupled anode electrode and grid and a resistorconnected between that grid and said means to apply positive operatingpotential.

2. A frequency stable multivibrator circuit including a pair of electrondischarge devices each having at least cathode, grid and anodeelectrodes, anode resistors and grid resistors coupled in series withthe individual gridanode paths of said electron discharge devices, meansto apply positive operating potential between said anode resistors and apoint of fixed reference potential, means to apply negative operatingpotential between said grid resistors and said point of fixed potential,means to yapply a potential intermediate said fixed and negativepotentials to the cathodes of said electron discharge devices, networkscross-coupling the anode electrode of one of said electron dischargedevices with the grid electrode of the other, said networks comprising aresistive and a capacitive element, electron discharge structures eachhaving a cathode, a grid and an anode, means to connect the cathodes tosaid point of xed reference potential, anode resistors individuallyconnecting the .anodes of said electron discharge structures to saidmeans to apply positive operating potential and to said point of fixedreference potential, capacitors individually coupling the anodes of saidelectron discharge structures to the grid electrodes of Said electrondischarge devices, and frequency determining networks individuallycoupling the anode electrodes of said electron discharge devices to thegrids of said electron discharge structures, said networks eachcomprising a capacitor connected between the coupled anode electrode andgrid and a resistor connected between that grid and means to applypositive operating potential.

3. A frequency stable multivibrator circuit including a pair of electrondischarge devices each having at least cathode, grid and anodeelectrodes, and having a given cut-oli grid-voltage characteristic,anode resistors and grid resistors coupled in series with the individualgridanode paths of said electron discharge devices, means to applypositive operating potential between said anode resistors and a point ofiixed reference potential, means to apply negative operative potentialbetween said grid resistors and said point of fixed potential, means toapply a potential intermediate said xed and negative potentials to thecathodes of said electron discharge devices, networks cross-coupling theanode electrode of one of said electron discharge devices with the gridelectrode of the other, said networks each comprising a resistor and acapacitor connected in parallel, diode elements individually connectedbetween the anode electrodes and said point of fixed referencepotential, electron discharge structures each having a cathode, a gridand an anode, and having a cut-oli characteristic -grid voltagesubstantially less than that of said electron discharge devices, meansto connect the cathodes to said point of fixed reference potential,anode resistors individually connecting the anodes of said electrondischarge structures to said means to apply positive operating potentialand to said point of fixed reference potential, capacitors individuallycoupling the anodes of said electron discharge structures to the gridelectrodes of said electron discharge devices, and frequency determiningnetworks individually coupling the anode electrodes of said electrondischarge devices to the grids of said electron discharge structures,said networks each comprising a capacitor connected between the coupledanode electrode and grid and a resistor connected between that grid andsaid means to apply positive operating potential.

4. A frequency stable multivibrator system comprising a pair of electrondischarge devices each having only cathode, grid, and anode electrodes,means to apply operating potentials to said anode and grid electrodes,crosscoupling networks coupling the anode electrode of each of saiddevices to the grid electrode of the other to form a bistablereciproconductive circuit, a pair of triggering electron dischargestructures each having a cathode, a grid, and an anode, connections fromthe last-mentioned cathodes to a point of fixed reference potential,connections individually coupling the anodes of said dischargestructures to said means, means coupling the anode of each of saiddischarge structures to the grid electrode of a respective dischargedevice, and frequency determining networks coupling the anode electrodeof each of said discharge devices to the grid of a respective dischargestructure and operating to determine the intervals during which saidcircuit is in each of its two stable states, said last-named means andsaid networks constituting crosscoupling means, each of said frequencydetermining networks comprising a series capacitor and a shunt resistor,connected between the anode electrode of one of said discharge devicesand the grid of the discharge structure coupled thereto,

5. A frequency stable multivibrator system comprising a pair of electrondischarge devices each having only cathode, grid, and anode electrodes,means to apply operating potentials to said anode and grid electrodes,cross-coupling networks coupling the anode electrode 0f each of saiddevices to the grid electrode of the other to form abistable'reciproconductive circuit, a pair of triggering electrondischarge structures each having a cathode, a grid, and an anode,connections from the lastmentioned cathodes to a point of fixedreference potential', connections individually coupling the anodes ofsaid discharge structures to said means, the arrangement being such thateach of said triggering structures has a cutoff grid voltagesubstantially less than that of said discharge devices, means couplingthe anode of each of said discharge structures to the grid electrode ofa respective discharge device, and frequency determining networkscoupling the anode electrode of each of said discharge devices to thegrid of a respective discharge structure and operating to determine theintervals during which said circuit is in each of its two stable states,said lastnamed means and said networks constituting crosscoupling means,each of said frequency determining networks comprising a seriescapacitor and a shunt resistor, connected between the anode electrode ofone of said discharge devices and the grid of the discharge structurecoupled thereto.

6. A frequency stable multivibrator system comprising a pair of electrondischarge devices each having only cathode, grid, and anode electrodes,means to apply operating potentials to said anode and grid electrodes,crosscoupling networks coupling the anode electrode of each of saiddevices to the grid electrode of the other to form a bistablereciproconductive circuit, each of said networks comprising a resistor;a pair of triggering electron discharge structures each having acathode, a grid, and an anode, connections from the last-mentionedcathodes to a point of ixed reference potential, connectionsindividually coupling the anodes of said discharge structures to saidmeans, the arrangement being such that each of said triggeringstructures has a cutoff grid voltage substantially less than that ofsaid discharge devices, means coupling the anode of each of saiddischarge structures to the grid electrode of a respective dischargedevice, and frequency determining networks coupling the anode electrodeof each of said discharge devices to the grid of a respective dischargestructure and operating to determine the intervals during which saidcircuit is in each of its two stable states, said last-named means andsaid networks constituting cross-coupling means, each of said frequencydetermining networks comprising a series capacitor and a shunt resistor,connected between the anode electrode of one of said discharge devicesand the grid of the discharge structure coupled thereto.

7. A frequency stable multivibrator system comprising a pair of electrondischarge devices each having only cathode, grid, and anode electrodes,means to apply operating potentials to said anode and grid electrodes,crosscoupling networks coupling the anode electrode of each of saiddevices to the grid electrode of the other to form a bistablereciproconductive circuit, one of said networks comprising a resistorand the other comprising a capacitor; a pair of triggering electrondischarge structures each having a cathode, a grid, and an anode,connections from the last-mentioned cathodes to a point of fixedreference potential, connections individually coupling the anodes ofsaid discharge structures to said means, the arrangement being such thateach of said triggering structures has a cutoff grid voltagesubstantially less than that of said discharge devices, means couplingthe anode of each of said discharge structures to the grid electrode ofa respective discharge device, and frequency determining networkscoupling the anode electrode of each of said discharge devices to thegrid of a respective discharge structure and operating to determine theintervals during which said circuit is in each of its two stable states,said last-named means and said networks constituting cross-couplingmeans, each of said frequency determining networkscomprising a seriescapacitor and a shunt resistor, connected between theanode electrode ofone of said discharge devices and the grid of the discharge structurecoupled thereto.

8. A frequency stable multivibrator system'comprising a pair of electrondischarge devices each having only cathode, grid, and anode electrodes,means to apply operating potentials to said anode and grid electrodes,cross-coupling networks coupling the anode electrode of each of saiddevices to the grid electrode of the other to forni a bistablereciproconductive circuit, each of said networks. comprising acapacitor; a pair of triggering electron discharge structures eachhaving a cathode, a grid, and an anode, connections from thelast-mentioned cathodes to a point of xed reference potential,connections individually coupling the anodes of said dischargestructures to said means, the arrangement being such that each of saidtriggering structures has a cutoff grid Voltage substantially less thanthat of said discharge devices, means coupling the anode of each of saiddischarge structures to the grid electrode of a respective dischargedevice, and frequency determining networks coupling the anode electrodeof each of said discharge devices to the grid of a respective dischargestructure and operating to determine the intervals during which saidcircuit is in each of its two stable states, said last-named means andsaid networks constituting cross-coupling means, each of said frequencydetermining networks comprising a series capacitor and a shunt resistor,connected between the anode electrode of one of said discharge devicesand the grid of the discharge structure coupled thereto.

9. A frequency stable multivibrator system comprising a pair of electrondischarge devices each having only cathode, grid, and anode electrodes,means to apply operating potentials to said anode and grid electrodes,crosscoupling networks coupling the anode electrode of each of saiddevices to the grid electrode of the other to form a bistablereciproconductive circuit, one of said networks comprising a capacitorand a resistor connected in parallel and the other comprising acapacitor; a pair of triggering electron discharge structures eachhaving a cathode, a grid, and an anode, connections from thelast-mentioned cathodes to a point of lixed reference potential,connections individually coupling the anodes `of said dischargestructures to said means, the arrangement being such that each of saidtriggering structures has a cutot grid voltage substantially less thanthat of said discharge devices, means coupling the anode of each of saiddischarge structures to the. grid electrode of a respective dischargedevice, and frequency determining networks coupling the anode electrodeof each of said discharge devices to the grid of a respective dischargestructure and operating to determine the intervals during which saidcircuit is in each of its two stable states, said last-named means andsaid networks constituting cross-coupling means, each of said frequencydetermining networks comprising a series of capacitor and a shuntresistor, connected between the anode electrode of one of said dischargedevices and the grid of the discharge structure coupled thereto.

l0. A frequency stable multivibrator system comprising a pair ofcross-coupled electron discharge devices each having only cathode, grid,and anode electrodes, said devices forming a bistable reciproconductivecircuit, means to apply operating potentials to said anode and gridelectrodes, a pair of triggering electron discharge structures eachhaving a cathode, a grid, and an anode,

individually cross-coupled to Vsaid discharge devices, connections fromthe last-mentioned cathodes to a point of fixed reference potential,connections individually coupling the anodes of said dischargestructures to said means, and frequency determining networks interposedin said individual cross-coupling connections and operating to determinethe intervals during which said circuit is in each of its two stablestates, each of said networks 9 comprising a series capacitor and ashunt resistor connected between the anode electrode of one of saiddischarge devices and the grid of the associated discharge structure.

11. A frequency stable multivibrator circuit comprising a pair ofcross-coupled electron discharge devices each having only cathode, grid,and anode electrodes and having a given cutoC grid voltage, means toapply operating potentials to said anode and grid electrodes, a pair oftriggering electron discharge structures each having a cathode, a grid,and an anode, individually cross-coupled to said discharge devices,connections from the lastmentioned cathodes to a point of fixedreference potential, connections individually coupling the anodes ofsaid discharge structures to said means, the arrangement being such thateach of said discharge structures has a cuto grid voltage substantiallyless than that of said discharge devices, and frequency determiningnetworks interposed in said individual cross-coupling connections, eachof said networks comprising a series capacitor and a shunt resistorconnected between the anode electrode of one of said discharge devicesand the grid of the associated discharge structure.

12. A frequency stable multivibrator circuit comprising a pair ofelectron discharge devices each having only cathode, grid, and anodeelectrodes, means to apply operating potentials to said anode and gridelectrodes, cross coupling networks coupling the anode electrode of eachof said devices to the grid electrode of the other, said networkscomprising resistive and capacitive elements; a pair of electrondischarge structures each having a cathode, a grid, and an anode,connections from the lastmentioned cathodes to a point of xed referencepotential, connections individually coupling the anodes of saiddischarge structures to said means, capacitors coupling the anode ofeach of said discharge structures to the grid electrode of a respectivedischarge device, and frequency determining networks coupling the anodeelectrode of each of said discharge devices to the grid of a respectivedischarge structure, said capacitors and said networks constitutingcross-coupling means, each of said frequency determining networkscomprising a capacitor connected between the coupled anode electrode andgrid and a resistor connected between that grid and said first-namedmeans.

References Cited in the le of this patent UNITED STATES PATENTS

